The invention relates to a multistage transmission for a motor vehicle.
From DE 10 2008 055 626 A1 a multistage transmission for a motor vehicle, which is designed for selecting nine forward transmission gears, with different step-up ratios, is known. The multistage transmission of DE 10 2008 055 626 A1 comprises four operatively interconnected planetary gear stages, a transmission input shaft for attaching to an internal combustion engine, a transmission output shaft for attaching drive wheels, three clutch units, each of which comprises two clutch elements and three brake units, each of which comprises one clutch element.
The object of the invention is in particular to provide a compact multistage transmission providing high flexibility and high efficiency.
According to the invention, a multistage transmission, in particular for a motor vehicle, the transmission being provided at least structurally for selecting at least twelve forward transmission gears with different step-up ratios, with four operatively interconnected planetary gear stages, with a transmission input shaft for attaching to an internal combustion engine, with a transmission output shaft, for attaching to drive wheels, with four clutch units, each of which comprises two clutch elements, and with three brake units, each of which comprises one clutch element, is proposed.
By such a configuration of a multistage transmission, a compact multistage transmission with twelve forward transmission gears and three reverse transmission gears may be provided, which on the one hand has a very high flexibility and a high power-shifting capability and on the other hand a high efficiency. Rotation speed and torque factors of transmission elements of multistage transmission, in particular of planet gear carriers, may be reduced, at least in part by an embodiment of the invention, whereby the stresses on transmission elements may be reduced. Moreover, a low relative speed in at least one open clutch unit and/or in at least one open brake unit may be obtained. Due to the inventive configuration of the multistage transmission, at least one of the clutch units and/or at least one of the brake units may be provided with a form fitting switching, so that a multistage transmission with reduced drag losses may be provided. Furthermore, a particularly high spread, in particular greater than 11, can be achieved between the first forward gear and the last forward gear. Moreover, a hybrid functionality with one or two electric motors and/or a four-wheel drive functionality may be easily implemented.
A “clutch unit” should in particular be understood as a switching unit, which is arranged in a power flow between two of the planetary gear stages and which is provided to connect its two non-rotatably mounted clutch elements, which are independently rotatable in an open state, in a closed state, in a rotationally fixed relationship to each other. A “brake unit” should in particular be considered as a switching unit, which is operatively arranged between one of the planetary gear stages and a transmission housing, and which is provided to connect its rotatable clutch element, which, in an open state, may be rotated independently from the transmission housing, with transmission housing, in a closed state, in a non-rotatable way. By “rotationally fixed connection,” a connection is to be understood, in particular wherein a power flow, averaged over a complete rotation, is transmitted with an unchanged torque, an unchanged direction of rotation and/or an unchanged speed.
The clutch units are preferably operatively arranged between the planetary gear stages, so that in the closed state at least two transmission elements of planetary gear stages are non non-rotatably fixed to each other. The brake units are respectively arranged operatively between one of the planetary gear stages and the transmission housing, so that, in the closed state, at least one transmission element of the planetary gear stage is non non-rotatably connected with the transmission housing. In this context, a clutch unit is not considered, in particular, a clutch unit, which is arranged before the first or after the fourth planetary gear stage. A “clutch unit which is arranged before the first planetary gear stage” in a particularly preferred embodiment, is a clutch unit, which in at least one transmission gear, is arranged in a power flow between the internal combustion motor and the transmission input shaft. A “clutch unit or brake unit, which is arranged after the fourth planetary gear stage,” in a particularly preferred embodiment, is a clutch unit, or brake unit, which, in at least one transmission gear, is arranged in a power flow between the transmission output shaft and an axle drive, as for example, in a four-wheel clutch. Basically, the switching capability of the multistage transmission may be increased by a clutch unit, which is arranged in an upstream position with respect to the first planetary gear stage and/or by a clutch unit which is arranged in a downstream position with respect to the fourth planetary gear stage.
“Structurally provided for switching a transmission gear” means in particular that by means of the clutch units and brake units a corresponding transmission gear may be mechanically realized, in principle, irrespective of the fact that in the context of a switching strategy, the selection of the gear is omitted or not. “Provided” means in particular programmed, equipped, configured and/or arranged.
Since the multistage transmission comprises four clutch units and three brake units, the multistage transmission comprises a total of seven switching units. In an advantageous embodiment, at least one of the switching units, in particular at least two of the switching units, are provided with a form fit. Thereby, the drag loss may be minimized, whereby the power loss in the multistage transmission may be reduced. Preferably, one of the clutch units is a form-fitting switching unit. In particular, additionally or alternatively, at least one of the brake units is a form-fitting switching unit.
A “form-fitting switching unit” means, in particular, a switching unit, which is provided with a toothing and/or claws for connecting its clutch elements or for attaching its clutch element, wherein the toothing or claws form-fittingly engage for providing a rotationally fixed connection, wherein the transmission of a power flow in a completely closed state at least substantially take place by means of a form fit. The seen switching units may be substantially made by friction of form fit. A “frictionally engaged switching unit” is in particular a switching unit, which, for connecting its clutch elements or for attaching its clutch element, is provided with at least two friction partners, which, for providing a rotationally fixed connection, are frictionally contacting each other, wherein the transmission of a power flow in a completely closed state, takes place at least substantially by friction. A frictionally configured clutch unit is preferably a multi-plate clutch unit, and a frictionally configured brake unit is preferably a clawed brake unit. A formfitting switching unit is advantageously switchable by means of a sliding sleeve. A formfitting switching unit may be provided with or without a synchronization.
Preferably, the multistage transmission comprises actuators for the automatic connection of the clutch units and brake units. In principle, it is also possible, that at least a portion of the clutch units and/or the brake units are at least partially self-switching. An independent self-switching clutch unit and brake unit is in particular designed as a freewheel. It is also possible, in principle, to form at least one part of the clutch units and/or the brake units as each a combination of a frictional switching unit and an independent self-switching unit or as each a combination of a form-fitting switching unit and an independent self-switching unit.
The four planetary gear stages are preferably constructed as a first, a second, a third and a fourth planetary gear stage. Preferably, the planetary gear stages are arranged behind one another along a main axis of rotation. The numbering of the planetary gear stages as “first,” “second,” “third” and “fourth” represent, when viewed along an axial direction originating from the engine axial direction, in particular a sequence of an axial arrangement of planetary gear stages, wherein along the direction originating from the internal combustion engine, with respect to the other three planetary gear stages, the first planetary gear stage occupies a first, i.e. foremost axial position, the second planetary gear stage a second axial position following the first axial position, the third planetary gear stage a third axial position subsequent to the second axial position, and the third planetary gear stage a fourth axial position, subsequent to the third axial position, i.e. the rearmost axial position. Basically, however, a spatial rearrangement of the planetary gear stages, for example, in a stacked configuration, is also conceivable. A spatial rearrangement by a modified arrangement of clutch units and/or brake units or a modified arrangement of the intermediate shafts of the multistage transmission is also fundamentally possible.
For simplification, a “first, second, third or fourth planetary gear stage” has to be also construed as a first, second, third or fourth planet gear carrier associated with the first, second, third or fourth planetary gear stage, respectively. Correspondingly, a “first, second, third or fourth sun gear” and a “first, second, third or fourth ring gear” should be considered as a sun gear associated to the first, second, third or fourth planetary gear stage or a ring gear associated to the first, second, third or fourth planetary gear stage, respectively. For example, the first planet gear carrier has to be considered as a planet gear carrier of the first planetary gear stage.
Preferably, at least one of the clutch units is provided for blocking a planetary gear stage. “Blocking a planetary gear stage” means in particular that the sun gear, the planet gear carrier and the ring gear of a single planetary gear stage are rotationally fixed to each other, whereby in such an operating state, they have the same speed and the same direction of rotation. A “clutch unit, provided for blocking a planetary gear stage” is considered as a blocking clutch unit, by which by closing only this clutch unit, the corresponding planetary gear stage may be blocked. To this end, the blocking clutch unit may be selectively arranged between the sun gear and the planet gear carrier or between the sun gear and the ring gear or between the planet gear carrier and the ring gear, of a respective planetary gear stage.
The embodiment of a multistage transmission, which is described in the following, represents a particular example, which has, in principle, further kinematically equivalent examples. For example, in particular, the planetary gear stages, as shown in the following, may be single planet gear sets. A kinematic equivalent is also the case when at least one of the planetary gear stages is a double planet gear set, whereby, in order to have the same kinematic operation, only the gear ratio of the planetary gear stage has to be adjusted. Moreover, in principle, also a connection of a sun gear and a planet gear carrier or of a ring gear and of a planet gear carrier or of a sun gear with a ring gear may be swapped, without changing the kinematic of the multistage transmission.
The terms “axial” and “radial” are referred, in the following, in particular, to the main rotation axis of the multistage transmission, so that the expression “axial” indicated, in particular, a direction, which is parallel or coaxial to the main rotation axis. The expression “radial” also indicates a direction which is perpendicular to the main rotation axis.
Further advantages result from the following description of the figures. In the figures, an embodiment of the invention is shown. The figures, the figure description and the claims contain numerous features in combination. Those skilled in the art will consider the features expediently also individually and combine them into additional, meaningful combinations.